1. Field of the Invention
The present invention relates to a MEMS switch employing a piezoelectric sensor, and more particularly, to a method of enlarging a travel of a piezoelectric sensor and a MEMS switch employing the enlarged travel of a piezoelectric sensor.
2. Description of the Related Art
Conventionally, a micro-electromechanical systems (MEMS) switch can be classified by means of an employed actuator into four types, such as dynamo-electrostatic, thermal expansion, dynamo-electromagnetic and piezoelectric types, and by means of a switching direction into two types, such as vertical contact and lateral contact types.
Firstly, the dynamo-electrostatic type of MEMS switch uses a curved surface electrode type or comb drive type. This kind of switch is mostly developed nowadays. This type of MEMS switch employs the principles that two electrodes are contacted when different polarity of voltages are applied to the two electrodes of which one is a stationary electrode and the other is a movable electrode spaced apart from the stationary electrode.
Generally, the manufacture of this type of switch is not difficult; however, it additionally needs the use of a chip for raising the voltage to be useful for the current RF devices due to the requirement of at least several decades of voltage, thereby increasing the manufacturing cost. The travel speed of the switch has a range of 1 to 200 seconds depending upon its structure.
Secondly, the dynamo-electromagnetic type of MEMS switch uses the theory of an electromagnet, which makes a magnetic field through a coil structure. While this type of switch can be operated by a relatively low voltages of about 5 Volts, when the structure of the switch becomes complex and hug, its power consumption comes to reach a number of hundreds mW.
The thermal expansion type of MEMS switch uses the theory that the volume of solid or liquid materials expands as its temperature increases. While a relatively low voltage of about 5 Volts can also operate this type of switch, this switch is very sensitive to an ambient temperature, its power consumption comes to reach a number of hundreds of mW, and conclusively its travel speed is too slow such that it becomes several decades of milli-seconds.
The piezoelectric type of MEMS switch uses the theory of piezoelectric materials of which volume is expanded when a voltage is applied. While this type of switch has the most prompt travel speed (100 nsec to 1 sec) among the abovementioned methods, the most large power can transmit when it drives, and, while it can be driven by a relatively low voltage, this strain can be a maximum of 0.1% of the length of the materials, thus, the use of the MEMS switch has a disadvantage that its travel length is no more than several decades or hundreds of nanometers.
In this connection, the raising of the operation voltage implies difficulties in adoption of a portable optical communication device or personal communication services, or the requirement of additional cost due to the sue of the voltage-raising device.
High level of power consumption means the reduction of working period per one charge of portable devices such as PCS, leapt computer, etc. The more the speed of data communication is accelerated, the more the need of the component having a prompt travel speed is increased. Furthermore, in RF applications such as PCS, laptop, WLAN etc., in which various approaches for integrating all components in one chip are accomplished, those skilled in the art are interested in MEMS components having a relatively small area.
MEMS is a technology of combining a computer and a very small mechanical device such as a sensor, a valve, a gear, a reflection mirror and a driver etc. mounted in the semiconductor chip. It is used as a vibration accelerator in an air-bag for an automobile A MEMS device comprises a micro circuit on a very small silicon chip which a part of mechanical devices have been manufactured.
Further examples of applications of MEMS include GPS sensors for tracking express parcel services and detecting a intermediate parcel treatment process; a sensor mounted on wings of an airplane provided with a number of tiny auxiliary ailerons for detecting and reacting to air flow depending upon variations of surface resistance of the wings of an airplane; and optical exchanging devices capable of exchanging optical signals to an individual passageway at a speed of 20 nsec.
As described hereinabove, while the piezoelectric type MEMS switch is capable of nearly solving the aforementioned problems since it allows a lowering of voltage and power consumption, and a raising of travel speed, since a travel length for a voltage below 5 volts is too small, it is impossible to apply the variable optical device such as optical switch, RF switch, filter, etc.
Eventually, the present invention provides a method of enlarging a travel length of the piezoelectric materials while its travel mechanism using a piezoelectric material is used as before.